Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $83.58   12.110%   $93.7015   $93.70   $93.70   $93.70  
  Purchase #2 $196.52   9.844%   $215.8654   $215.87   $215.85   $215.90  
  Purchase #3 $28.45   7.371%   $30.547   $30.55   $30.55   $30.50  
  Purchase #4 $153.48   12.464%   $172.6097   $172.61   $172.60   $172.60  
  Purchase #5 $13.56   3.416%   $14.0232   $14.02   $14.00   $14.00  
  Purchase #6 $111.54   11.118%   $123.941   $123.94   $123.95   $123.90  
  Purchase #7 $68.31   12.641%   $76.9451   $76.95   $76.95   $76.90  
  7 purchase totals = $655.44       $727.6329   $727.64   $727.60   $727.50